Hi,
Can somebody explain me the reason why model save() method doesn't
respect database settings?
I have case with foreign key defined like this:
class Measurements(models.Model):
customer = models.ForeignKey(Customer, on_delete=models.SET_NULL,
*blank=True, null=True*)
order = models.ForeignKey(Order, on_delete=models.SET_NULL,
*blank=True, null=True*)
Also Customer model itself has foreign key to Measurements:
class Customer(models.Model):
measurements = models.ForeignKey(Measurements,
on_delete=models.CASCADE)
I need this hack to create model form set for a customer. Measurements
must have foreign key to it for this to work. But unfortunately save
method doesn't respect my settings. It force me to assign customer to
measurements where customer itself cannot be created because it requires
measurements. The thing is i don't really care about connection from
measurements side. This is the reason why it allowed to be null.
So, for now i just override save() method for Measurements model and add
check for the null attribute. Like this:
if *field.null is not True* and obj and obj.pk is None:
# Remove the object from a related instance cache.
if not field.remote_field.multiple:
field.remote_field.delete_cached_value(obj)
raise ValueError("save() prohibited to prevent data loss due to
unsaved related object '%s'." % field.name)
As you can see Measurements model has two such foreign keys. Where
Customer and Order must take leading part in pairs. There are cases
where i want keep "orphan" measurements. And looks like this is valid
case as soon as save() will start respect field settings.
Thank you in advice,
Roman
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